1. Field of the Invention
The present invention relates to protection of data stored in a storage volume, and more particularly to a protection system for data stored in a storage volume in a data processing system including a high order unit, such as a host computer, and a storage unit having the storage volume, such as a magnetic disc pack or a magnetic tape, which is accessible by the high order unit.
2. Description of the Prior Art
When the host computer accesses the data stored in the storage volume loaded in the storage unit, it may improperly access data in the storage volume. In order to prevent such improper accessing and protect the data in the storage volume, the following methods have been commonly used.
In a first method, areas in the storage volume are protected for each data set. In a typical example, a password is checked by a program in the host computer, or a range of input/output addresses is checked. However, in those methods, information for checking whether the access is improper or not is stored in main memory of the host computer. Accordingly, when a program capable of updating the content of the main memory, a program capable of referring to a password area or a program capable of invalidating checking of an access range is executed improperly or an error occurs, the leakage of the data and destruction of the data cannot be prevented.
In a second method, an entire storage volume is protected volume by volume. A typical example is write protection using a write protection switch arranged on a control panel of the storage unit. However, since read protection is not effected in such an arrangement, the protection of the data for each data set in the first method must be employed to provide protection for the leakage of the data. Further, if an operator forgets to set the write protection switch, there is a risk of destroying the volume. U.S. Pat. No. 4,434,464 discloses such a method for protecting data.